Let's say we have a fantasy society that is...mm...post-Renaissance, just starting to crawl into the opening throes of the industrial revolution. It's advanced enough to have mental asylums and a fair number of drugs, but psychiatry is still largely in its infancy, and like China, we have fireworks but no guns. Like Rome, it is an advanced society that is still in danger of being toppled by screaming barbarians wearing bits of leather and carrying swords.
Let us say, further, that our heroine has fetched up in the basement of one of the aforementioned screaming barbarians, who used to be some kind of shaman, but following the utter annhilation of his civilization is ekeing out a living selling cures for the clap. (Yes, he's bitter. Unbelievably bitter.)
Because our heroine has a peculiar mental/magical malady the likes of which the good doctor has not seen before, he throws his hands in the air and says in effect "Okay, I'll do my best, but we're gonna have to run some tests, and that means I need a blood sample."
Science is about two-thirds alchemy at this point, so a jab in the fingertip ain't gonna do it. He needs at least a beaker's worth of blood.
The hypodermic needle was not invented until the 1800s, but intravenous injections and blood transfusions are reported as far back at the 1600's. Except that I can't figure out how they did it. They say "bladders of animals" were used, but used HOW?
How, dear readers, do we get a blood sample with our available technology?
All I can think of at the moment is that he ties off her arm junkie style and jams a hollow metal skewer of some sort into a vein, then either hooks a tube on the end and lets circulation carry the rest, or siphons it off with some kind of primitive bell jar. (Except that I'm not quite sure how that would work, I just remember reading about it in some kind of primitive medical thing somehow.)
It's going to be pretty damn painful no matter what, I imagine, but I solicit your suggestions as to how it actually works.